Antireflection film and display apparatus comprising the same

ABSTRACT

The present invention is directed to an antireflection film having a multilayer structure in which an antireflection multilayer film including at least two thin films is formed on a substrate, wherein at least one of the thin films contains a coloring agent. The antireflection multi-layer film absorbs light of an entire range of wavelength of 400-700 nm, and the reflectance of the antireflection multi-layer film with regard to the wavelength, light of which this antireflection multi-layer film can absorb, is smaller than the reflectance of the substrate. The antireflection film can be applied to a cathode ray tube or a light-transmitting display substrate of a display apparatus such as a liquid crystal display apparatus for the purpose of effectively avoiding reflection of external light.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an antireflection film for effectivelypreventing external reflection, and a display apparatus having theantireflection film.

2. Description of the Related Art

A glass plate is generally used as a substrate for a window glass, ashow window, or the display surface of a display device. The glass platesometimes causes specular reflection of ambient light such as daylightor light from lighting units. For this reason, a reflection oftenoccurs, resulting in deterioration in transparency. Especially in adisplay apparatus, if specular reflection occurs on the display surface,an image to be displayed on the display surface overlaps an image of alight source, a scene, and the like to cause considerable deteriorationin image quality.

In a conventional method of preventing such reflection, a single-layeror multilayer optical film, i.e., an antireflection film, is formed onthe substrate surface to prevent external reflection by usinginterference of light.

One well-known antireflection film is referred to as 1/4-wave film. This1/4-wave film will be described below.

When external reflection is to be prevented by a single-layerantireflection film, the following non-reflection conditions must besatisfied, provided that the refractive index of air is represented byn₀ ; the refractive index of the thin film, n₁ ; the refractive index ofthe substrate, n₂ ; the thickness of the thin film, d; and thewavelength of light which is to be prevented from reflecting, λ.

    n.sub.l d=λ/4                                       (1)

    n.sub.1.sup.2 =n.sub.0 n.sub.2                             ( 2)

Since the thickness of the thin film which satisfies these equations (1)and (2) corresponds to 1/4 the wavelength of the light which is to beprevented from reflecting, the film is called a 1/4-wave film.

When the equations (1) and (2) are satisfied, the reflection of thelight having a wavelength of λ can be reduced to zero. When a glasssubstrate is used, n₂ is 1.52, and the refractive index n₀ of the air is1.00. Therefore, the refractive index n₁ of the thin film must be set tobe 1.23. The most practicable low-refractive-index material of currentlyknown thin film materials is MgF₂. The refractive index of MgF₂ is 1.38,which is larger than the refractive index (n₁ =1.23) defined by thenon-reflection conditions. For this reason, it is impossible tocompletely prevent external reflection by using only a single-layeredlow-refractive-index thin film.

Under the circumstances, attempts have been made to prevent reflectionby forming a two-layer antireflection film consisting of lower and upperlayers formed on a substrate. With this film, the followingnon-reflection conditions must be satisfied, provided that therefractive index of air is represented by n₀ ; the refractive index ofthe upper layer, n₃ ; the refractive index of the lower layer, n₄ ; therefractive index of the substrate, n₂ ; the thickness of the upperlayer, d₁ ; the thickness of the lower layer, d₂ ; and the wavelength oflight which is to be prevented from reflecting, λ.

    n.sub.3 d.sub.1 =λ/4                                (3)

    n.sub.4 d.sub.2 =λ/4                                (4)

    n.sub.2 n.sub.3.sup.2 =n.sub.0 n.sub.4.sup.2               ( 5)

According to these equations (3), (4), and (5), if the substrate is aglass plate, since n₂ =1.52 and n₀ =1.00, external reflection can beprevented by selecting materials for the lower and upper layers suchthat a refractive index ratio n₄ /n₃ is set to be 1.23.

It is known that an antireflection film having not only two layers, butthree or more layers may be used for controlling the reflection in awide range. More specifically, the thickness of an antireflection filmis determined by the wavelength of the light. Therefore, theoretically,by use of a multilayer having an N-number of layers, the reflectancerelating to each of an N-number of wavelengths can be decreased.

Published Unexamined Japanese Patent Application No. 3-261047 disclosesa conventional method, wherein a two-layer antireflection film is used,and the refractive index of the lower layer is controlled by adjustingthe porosity thereof. Further, it is proposed to add pigments to thetwo-layer antireflection film so that it will have an optical filtereffect.

As described, it is known that a multilayer antireflection film shouldbe formed on a glass substrate surface in order to reduce externalreflection.

Regardless of its type, the conventional multilayer antireflection filmhas a structure in which materials having high and low refractiveindices are formed on a glass substrate. This is because therefractivity of the multilayer film had to be set at a certain value inorder to satisfy the non-reflection conditions for a specificwavelength. However, there are only a limited number of practicable low-and high-refractivity materials, and appropriate combinations must beselected from the limited number of the materials. Examples of thehigh-refractivity material are TiO₂, ZrO₂, BaO, SnO₂ ; examples of thelow-refractivity type are MgF₂, SiO₂, and SnO₂. The selection must bemade from these materials.

In addition, when the layers of the multilayer film are made ofdifferent materials as described above, the problem of adherence betweenlayers arises. As a result, the conditions for forming a film must becomplicatedly restricted.

SUMMARY OF THE INVENTION

The present invention has been proposed in consideration of theabove-described problem, and an object thereof is to provide anantireflection film having a multilayer structure.

Another object of the present invention is to provide a display devicecomprising such an antireflection film on its display surface.

According to the present invention, there is provided an antireflectionfilm having a multilayer structure in which an antireflection multilayerfilm including at least two thin films is formed on a substrate, whereinat least one of the thin films contains a coloring material and whereinthe antireflection multilayer film absorbs light of an entire range ofwavelength of 400-700 nm, and the reflectance of the antireflectionmultilayer film with regard to that wavelength, light of which theantireflection multilayer film can absorb, is smaller than thereflectance of the substrate.

Further, according to the present invention, there is provided a displaydevice comprising a light-transmissible display substrate and anantireflection multilayer film including at least two thin filmslaminated on the substrate, wherein at least one of the thin filmscontains a pigment and wherein the antireflection multilayer filmabsorbs light of an entire range of wavelength of 400-700 nm, and thereflectance of the antireflection multilayer film with regard to thatwavelength, light of which this antireflection multilayer film canabsorb, is smaller than the reflectance of the substrate.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed out in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate presently preferred embodiments ofthe invention, and together with the general description given above andthe detailed description of the preferred embodiments given below, serveto explain the principles of the invention.

FIG. 1A is a graph showing the spectral reflectance of an antireflectionmultilayer film according to Example 1;

FIG. 1B is a graph showing the spectral transmittance characteristics ofan antireflection multilayer film according to Example 1;

FIG. 2A is a graph showing the spectral reflectance of an antireflectionmultilayer film according to Example 2;

FIG. 2B is a graph showing the spectral transmittance characteristics ofan antireflection multilayer film according to Example 2;

FIG. 3A is a graph showing the spectral reflectance of an antireflectionmultilayer film according to Example 3;

FIG. 3B is a graph showing the spectral transmittance characteristics ofan antireflection multilayer film according to Example 3;

FIG. 4A is a graph showing the spectral reflectance of an antireflectionmultilayer film according to Example 4;

FIG. 4B is a graph showing the spectral transmittance characteristics ofan antireflection multilayer film according to Example 4;

FIG. 5A is a graph showing the spectral reflectance of an antireflectionmultilayer film according to Example 5;

FIG. 5B is a graph showing the spectral transmittance characteristics ofan antireflection multilayer film according to Example 5;

FIG. 6A is a graph showing the spectral reflectance of an antireflectionmultilayer film according to Example 6;

FIG. 6B is a graph showing the spectral transmittance characteristics ofan antireflection multilayer film according to Example 6;

FIG. 7A is a graph showing the spectral reflectance of an antireflectionmultilayer film according to Example 7;

FIG. 7B is a graph showing the spectral transmittance characteristics ofan antireflection multilayer film according to Example 7;

FIG. 8A is a graph showing the spectral reflectance of an antireflectionmultilayer film according to Example 8;

FIG. 8B is a graph showing the spectral transmittance characteristics ofan antireflection multilayer film according to Example 8;

FIG. 9A is a graph showing the spectral reflectance of an antireflectionmultilayer film according to Example 9;

FIG. 9B is a graph showing the spectral transmittance characteristics ofan antireflection multilayer film according to Example 9;

FIG. 10 is a partial sectional view showing a brief structure of acathode ray tube according to Example 10; and

FIG. 11 is a sectional view showing a brief structure of a liquidcrystal apparatus according to Example 11.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to the present invention at least one layer of theantireflection multilayer film contains a coloring material. Generally,a coloring material selectively absorbs light having a particularwavelength. Thin films containing such pigments were examined in detail,and the inventors have discovered the following.

Specifically, the refractive index of the thin film tends to increase inthe range of wavelength of light of which the coloring material absorbs,whereas the refractive index tends to decrease outside this range ofwavelength. Further, when an antireflection multilayer film is formed byuse of such thin films, the antireflection effect is significant in therange of wavelength in which the refractive index tends to increase,i.e. the range of wavelength which the coloring material absorbs.Consequently, the reflectance of the antireflection multilayer filmdecreases in the wavelength range which substantially corresponds to therange of the wavelength which the coloring material absorbs. Therefore,in the case where the antireflection effect is required in the entirerange of wavelength of visible light, the refractive index of theantireflection multilayer film must be increased in the entire range ofwavelength of visible light. As a result, it is necessary that theantireflection multilayer film absorbs the light in the entire range ofwavelength of visible light.

According to another result of the examination, in order for therefractive index to tend to increase in accordance with an increase inwavelength, the transmisitivity must be 95% or less, and in order tohave an increase in refractive index to such an extent that a sufficientresult can be obtained, the transmisitivity must be 90% or less, morepreferably, 85% or less.

Based on such findings, in the antireflection film having a multilayerstructure according to the present invention, it is possible to avoidthe reflection of visible light to the maximum degree by adding acoloring material which absorbs light in the entire range of wavelength,400-700 nm, to the films.

A usual multilayer antireflection film has a structure in which low- andhigh-refractive index layers are alternately laminated to have alow-refractive index layer at the outer surface. In a preferredembodiment of the present invention, it is possible to avoid thereflection of visible light effectively by adding a coloring material toa high-refractive index layer. The refractive index of a film varies inthe range of wavelength which the coloring material absorbs, asmentioned above, and therefore the refractive index can be set so as tosatisfy the non-reflection conditions for the antireflection multilayerfilm.

Therefore, it is preferable that at least one of even number-th layers,counting from the outermost layer of the multilayer antireflection film,contains a coloring material.

As described, the adjustment of the refractive index is conducted by thecoloring material which has a certain absorbing characteristic.Therefore it is no longer necessary to form each layer of the multilayerfilm of different materials such as low- and high-refractory types. Thelayers of the multilayer film can be made of the same material, therebyincreasing the adherence between layers.

Further, by using materials having different refractive indices, forexamples, SiO₂ and TiO₂ as low- and high-refractive materials,respectively, and further by adding a coloring material to the TiO₂layer, the antireflection effect can be improved.

Examples of the materials for the practicable thin film in the presentinvention are SiO₂, TiO₂, ZrO₂, TaO₅, and Al₂ O₃. The layers of themultilayer thin film may be made of different materials or the samematerial. When the same material is used, the adherence between layerscan be improved as mentioned above. However, in order to obtaincharacteristics of the multilayer structure, the layers should bedifferentiated from each other in the following ways. The coloringmaterial should be contained in some layers, and are not in otherlayers, the type of coloring material used should differ from one layerto another, and the contents of the coloring material should bedifferent from one layer to another.

When different materials are used for the layers of the thin film, it ispreferable that the uppermost layer is made of a low-refractivematerial.

In the present invention, black coloring materials including carbonblack and graphite can be used as coloring materials. Besides thesecoloring materials, almost all available pigments can be used. Examplesof the organic pigment are: azo-based yellow and red pigments such asBenzidine Yellow and Carmine FB, condensation pigments such as perylene,perylone, dioxazine, thioindigo, isoindolinone, quinophthalon, andquinacridone, and phthalocyanine-based pigments. Examples of theinorganic pigment are: titanium white, red iron oxide, chrome yellow,and cobalt blue. The pigments must be mixed such that the mixture has anabsorbance of 5% or more, preferable 10% or more, throughout the entirerange of wavelength of visible light.

As described above, the coloring material can be used in various ways.For example, a coloring material which absorbs light in the entire rangeof wavelength of visible light, such as carbon black or graphite, can beused solely, or such a coloring material can be used in combination withother coloring materials. Also, it is possible that a yellow or redcoloring material which absorbs the light in a wavelength of 500 nm or600 nm or less, such as Benzine Yellow or Carmine FB, is combined with ablue coloring material which absorbs the light in a wavelength of 500 nmor more, such as Heliogen blue EP-7.

It is preferable that coloring material which can be subjected to theabove-mentioned combinations be of the organic type because of itsvariety. Further, in order to keep a certain transparency of the film,the particle sizes of these coloring materials should preferably be nomore than 300 nm. In general, in order to obtain a certain transparency,the particle of a coloring material should be 1/2 or less of thewavelength λ, and therefore the wavelength should be no more than 200 nmin the case of visible light. This is because the transparency is likelyto deteriorate due to the scattering of light which is caused by apigment having a large particle size. According to the presentinvention, since coloring materials are confined in the film, thedifference of refractive index between coloring material and filmmaterial is smaller than that of refractive index between coloringmaterial and the air. Consequently, the particle size of the coloringmaterial may be allowable up to 300 nm to maintain the transparency ofthe film. Further, in order to prevent equation from a porous film andensure sufficient resistance to light, a pigment having a particle sizeof 3 nm or more is preferably used. More preferably, the particle sizeof a pigment should be 5-200 nm.

The amounts of pigment contained in thin films may differ greatly fromone another, depending on the type of pigment, and therefore it is noteasy to set a range of contents.

The antireflection multilayer film of the present invention can beapplied to those apparatuses in which an image is observed through adisplay substrate, such as cathode ray tube and liquid crystal displayapparatus.

Examples of the present invention will now be described in detail.

EXAMPLE 1

(1) Preparation of Lower Layer Forming Solution

First, a solution A having the following composition was prepared as alower-layer forming solution.

    ______________________________________                                        A:     Si(OC.sub.2 H.sub.5).sub.4 silicon tetraethoxide                                                  1.0 wt %                                                  pigment dispersion 1                                                                              6.2 wt %                                                  HNO.sub.3 nitric acid                                                                             0.1 wt %                                                  water               0.5 wt %                                                  IPA (isopropylalcohol)                                                                            balance                                            ______________________________________                                    

In this case, the pigment dispersion 1 was obtained by dispersing carbonblack (pigment 1) having an average particle size of 100 nm inisopropylalcohol at 2.4 wt %. The mixed solution prepared to have theabove composition A was agitated for about one hour to cause a reaction,thus preparing a lower layer forming solution.

(2) Preparation of Upper Layer Forming Solution

A solution B having the following composition was prepared as alower-layer forming solution.

    ______________________________________                                        B:     Si(OC.sub.2 H.sub.5).sub.4 silicon tetraethoxide                                                  1.0 wt %                                                  HNO.sub.3 (nitric acid)                                                                           0.1 wt %                                                  water               0.5 wt %                                                  IPA (isopropylalcohol)                                                                            balance                                            ______________________________________                                    

After the mixed solution prepared to have the above composition B, thesolution was agitated for about one hour to cause a reaction, thuspreparing a upper layer forming solution.

(3) Formation of Antireflection Multilayer Film

The above-described lower layer forming solution was coated on a glasssubstrate having a refractive index of 1.52 by dip coating method, andwas dried at 50° C. for 5 minutes to form a lower layer having athickness of about 0.1 μm. Subsequently, the upper layer formingsolution was coated on the lower layer, and was calcined in anatmosphere of 180° C. for 10 minutes to form an upper layer having athickness of about 0.1 82 m. The composition of each layer of thetwo-layer antireflection film was as follows.

    ______________________________________                                        Lower layer SiO.sub.2        66 wt %                                                      pigment 1 (carbon black)                                                                       34 wt %                                          Upper layer SiO.sub.2 only                                                    ______________________________________                                    

The spectral reflectance and spectral transmittance of the two-layerantireflection film obtained in this manner were measured, and theresults were as shown in FIG. 1A and FIG. 1B. It should be noted thatthe spectral reflectance of the antireflection film was measured byMCPD-1000 available from Otsuka Electronics k.k. A halogen lamp was usedas a light source to perform measurement at an incident angle of 0°, andthe reflectance of a portion of the substrate on which no antireflectionfilm was formed was assumed to be 100%.

Also, the spectral transmittance was measured by a spectrocolorimeterCM-1000 available from MINOLTA CAMERA CO., LTD. The measurement wasperformed on the sample which was placed on a white board. Themeasurement value was expressed by the square root of the ratio of thevalue of the antireflection multilayer film to the value of a portion onwhich no antireflection multilayer film was formed.

As is clear from FIG. 1A and FIG. 1B, the antireflection film of thisembodiment exhibited an excellent antireflection effect.

EXAMPLE 2

(1) Preparation of Lower Layer Forming Solution

First, a solution C having the following composition was prepared as alower layer forming solution.

    ______________________________________                                        C:     Si(OC.sub.2 H.sub.5).sub.4 silicon tetraethoxide                                                  1.0 wt %                                                  pigment dispersion 2                                                                              8.4 wt %                                                  HNO.sub.3 (nitric acid)                                                                           0.1 wt %                                                  water               0.5 wt %                                                  IPA (isopropylalcohol)                                                                            balance                                            ______________________________________                                    

In this case, the pigment dispersion 2 was obtained by dispersingpigment 1 (carbon black) having an average particle size of about 100nm, Heliogen blue EP-7S as pigment 2, and perylene-based violet aspigment 3, in isopropylalcohol at 1.71, 0.34, and 0.34 wt %,respectively. The mixed solution prepared to have the above compositionC was agitated for about one hour to cause a reaction, thus preparing alower layer forming solution.

(2) Formation of Antireflection Film

By use of the solution B of Example 1 as an upper layer formingsolution, an antireflection film was formed on a glass substrate. Thecoating method, the conditions, and the film thickness were as inExample 1. The composition of each layer of the two-layer antireflectionfilm thus formed was as follows.

    ______________________________________                                        Lower layer    SiO.sub.2 58.8 wt %                                                           pigment 1 29.4 wt %                                                           pigment 2  5.9 wt %                                                           pigment 3  5.9 wt %                                            Upper layer    SiO.sub.2 only                                                 ______________________________________                                    

The spectral reflectance and spectral transmittance of the two-layerantireflection film obtained in this manner were measured, and theresults were as shown in FIG. 2A and FIG. 2B. As is clear from FIG. 2Aand FIG. 2B, the antireflection multilayer film of this embodimentexhibited an excellent antireflection effect, as in the case of the filmof Example 1.

EXAMPLE 3

(1) Preparation of Lower Layer Forming Solution

First, a solution D having the following composition was prepared as alower layer forming solution.

    ______________________________________                                        D:     Si(OC.sub.2 H.sub.5).sub.4 silicon tetraethoxide                                                  1.0 wt %                                                  pigment dispersion 3                                                                              9.6 wt %                                                  HO.sub.3 nitric acid                                                                              0.1 wt %                                                  water               0.5 wt %                                                  IPA (isopropylalcohol)                                                                            balance                                            ______________________________________                                    

In this case, the pigment dispersion 3 was obtained by dispersingpigments 2 and 3 each having an average particle size of about 100 nm,dioxadine-based violet as pigment 4, and isoindolinone-based yellow aspigment 5, in isopropylalcohol at 0.6 wt % respectively. The mixedsolution prepared to have the above composition D was agitated for aboutone hour to cause a reaction, thus preparing a lower layer formingsolution.

(2) Formation of Antireflection Multilayer Film

By use of the solution B of Example 1 as an upper layer formingsolution, an antireflection multilayer film was formed on a substrate.The coating method, the conditions, and the film thickness were similarto those of Example 1. The composition of each layer of the two-layerantireflection film thus formed was as follows.

    ______________________________________                                        Lower layer    SiO.sub.2 55.6 wt %                                                           pigment 2 11.1 wt %                                                           pigment 3 11.1 wt %                                                           pigment 4 11.1 wt %                                                           pigment 5 11.1 wt %                                            Upper layer    SiO.sub.2 only                                                 ______________________________________                                    

The spectral reflectance and spectral transmittance of the two-layerantireflection film obtained in this manner were measured, and theresults were as shown in FIG. 3A and FIG. 3B. As is clear from theresults, the antireflection film of this example exhibited an excellentantireflection effect, as in the case of the film of Example 1.

EXAMPLE 4

(1) Preparation of Lower Layer Forming Solution

First, a solution E having the following composition was prepared as alower layer forming solution.

    ______________________________________                                        E:    Ti(OC.sub.3 H.sub.7).sub.4 titanium tetraisopropoxide                                                1.0 wt %                                               pigment dispersion 1   6.2 wt %                                               pentyl alcohol         5.0 wt %                                               IPA (isopropylalcohol) balance                                          ______________________________________                                    

In this case, the pigment dispersion 1 used was the same as that ofExample 1. The mixed solution prepared to have the above composition Ewas agitated for about one hour to cause a reaction, thus preparing alower layer forming solution.

(2) Formation of Antireflection Multilayer Film

By use of the solution B of Example 1 as an upper layer formingsolution, an antireflection film was formed on a glass substrate. Thecoating method, the conditions, and the film thickness were as inExample 1. The composition of each layer of the two-layer antireflectionfilm thus formed was as follows.

    ______________________________________                                        Lower layer    TiO.sub.2 65 wt %                                                             pigment 1 35 wt %                                              Upper layer    SiO.sub.2 only                                                 ______________________________________                                    

The spectral reflectance and spectral transmittance of the two-layerantireflection film obtained in this manner were measured, and theresults were as shown in FIG. 4A and FIG. 4B. As is clear from theresults, the antireflection film of this example exhibited an excellentantireflection effect, as in the case of the film of Example 1.

EXAMPLE 5

(1) Preparation of Lower Layer Forming Solution

First, a solution F having the following composition was prepared as alower layer forming solution.

    ______________________________________                                        F:    Ti(OC.sub.3 H.sub.7).sub.4 titanium tetraisopropoxide                                                1.0 wt %                                               pigment dispersion 3   9.6 wt %                                               pentyl alcohol         5.0 wt %                                               IPA (isopropylalcohol) balance                                          ______________________________________                                    

In this case, the pigment dispersion 3 used was the same as that ofExample 3. The mixed solution prepared to have the above composition Fwas agitated for about one hour to cause a reaction, thus preparing alower layer forming solution.

(2) Formation of Antireflection Film

By use of the solution B of Example 1 as an upper layer formingsolution, an antireflection multilayer film was formed on a substrate.The coating method, the conditions, and the film thickness were as inExample 1. The composition of each layer of the two-layer antireflectionfilm thus formed was as follows.

    ______________________________________                                        Lower layer    TiO.sub.2   55 wt %                                                           pigment 2 11.25 wt %                                                          pigment 3 11.25 wt %                                                          pigment 4 11.25 wt %                                                          pigment 5 11.25 wt %                                           Upper layer    SiO.sub.2 only                                                 ______________________________________                                    

The spectral reflectance and spectral transmittance of the two-layerantireflection film obtained in this manner were measured, and theresults were as shown in FIG. 5A and FIG. 5B. As is clear from theresults, the antireflection film of this example exhibited an excellentantireflection effect, as in the case of the film of Example 1.

EXAMPLE 6

(1) Preparation of Lower Layer Forming Solution

First, a solution G having the following composition was prepared as alower layer forming solution.

    ______________________________________                                        G:     Si(OC.sub.2 H.sub.5).sub.4 silicon tetraethoxide                                                  1.0 wt %                                                  SnO.sub.2 -fine-particle dispersion                                                               14.4 wt %                                                 pigment dispersion 1                                                                              6.2 wt %                                                  HO.sub.3 (nitric acid)                                                                            0.1 wt %                                                  water               0.5 wt %                                                  IPA (isopropylalcohol)                                                                            balance                                            ______________________________________                                    

In this case, the SnO₂ fine-particle dispersion was obtained bydispersing fine particles of SnO₂ having a size of about 50-100 nm inIPA at 2 wt %. The pigment dispersion 1 used was the same as that ofExample 1. The mixed solution prepared to have the above composition Gwas agitated for about one hour to cause a reaction, thus preparing alower layer forming solution.

(2) Formation of Antireflection Multilayer Film

By use of the solution B of Example 1 as an upper layer formingsolution, an antireflection film was formed on a substrate. The coatingmethod, the conditions, and the film thickness were as in Example 1. Thecomposition of each layer of the two-layer antireflection film thusformed was as follows.

    ______________________________________                                        Lower layer    SiO.sub.2 39.7 wt %                                                           SnO.sub.2 39.7 wt %                                                           pigment 1 20.5 wt %                                            Upper layer    SiO.sub.2 only                                                 ______________________________________                                    

The spectral reflectance and spectral transmittance of the two-layerantireflection film obtained in this manner were measured, and theresults were as shown in FIG. 6A and FIG. 6B. As is clear from FIG. 6Aand FIG. 6B, the antireflection film of this example exhibited anexcellent antireflection effect, as in the case of the film ofExample 1. Further, this antireflection multilayer film had aconductivity, and its resistance was 10×10¹⁰ Ω/cm.

EXAMPLE 7

(1) Preparation of Upper Layer Forming Solution

First, a solution H having the following composition was prepared as aupper layer forming solution.

    ______________________________________                                        H:     Si(OC.sub.2 H.sub.5).sub.4 silicon tetraethoxide                                                  1.0 wt %                                                  SnO.sub.2 -fine-particle dispersion                                                               14.4 wt %                                                 HO.sub.3 (nitric acid)                                                                            0.1 wt %                                                  water               0.5 wt %                                                  IPA (isopropylalcohol)                                                                            balance                                            ______________________________________                                    

In this case, the SnO₂ fine-particle dispersion used was the same asthat of Example 6. The mixed solution prepared to have the abovecomposition H was agitated for about one hour to cause a reaction, thuspreparing a upper layer forming solution.

(2) Formation of Antireflection Multilayer Film

By use of the solution G of Example 6 as a lower layer forming solution,an antireflection multilayer film was formed on a substrate. The coatingmethod, the conditions, and the film thickness were as in Example 1. Thecomposition of each layer of the two-layer antireflection film thusformed was as follows.

    ______________________________________                                        Lower layer    SiO.sub.2 39.7 wt %                                                           SnO.sub.2 39.7 wt %                                                           pigment 1 20.5 wt %                                            Upper layer    SiO.sub.2 50.0 wt %                                                           SnO.sub.2 50.0 wt %                                            ______________________________________                                    

The spectral reflectance and spectral transmittance of the two-layerantireflection film obtained in this manner were measured, and theresults were as shown in FIGS.7A and 7B. AS is clear from the results,the antireflection film of this example exhibited an excellentantireflection effect, as in the case of the film of Example 1. Thisantireflection multi-layer film had a conductivity, and its resistancewas 5×10⁸ Ω/cm².

EXAMPLE 8

By use of solution B as a lower layer forming solution, solution A as amid-layer forming solution, and solution B as an upper layer formingsolution, an antireflection film having the three-layer structure wasprepared. The coating method, the conditions, and the film thicknesswere as in Example 1. The spectral reflectance and spectraltransmittance of the two-layer antireflection film obtained in thismanner were measured, and the results were as shown in FIG. 8A and FIG.8B. As is clear from the results, the antireflection film of thisexample exhibited an excellent antireflection effect in a region broaderthan that in the case of the film of Example 1.

EXAMPLE 9

By use of solution B as a lower layer forming solution, solution C as amid-layer forming solution, and solution B as an upper layer formingsolution, an antireflection film of the three-layer structure wasprepared. The coating method, the conditions, and the film thicknesswere as in Example 1. The spectral reflectance and spectraltransmittance of the two-layer antireflection film obtained weremeasured, the results being shown in FIGS. 9A and 9B. As is clear, theantireflection film of this example exhibited an excellentantireflection effect in a region broader than that in the case of thefilm of Example 2.

EXAMPLE 10

As another example of the display apparatus, the case in which thepresent invention is applied to a cathode ray tube will now bedescribed.

FIG. 10 is a partially cutaway section showing a cathode ray tube 60made according to the invention. The cathode ray tube has an airtightglass envelope 61 the interior of which is evacuated. The envelope 61includes a neck 62 and a cone 63 continuously extended from the neck 62.In addition, the envelope 61 has a faceplate 64 sealed by a frit glass.An explosion-proof metal-made tension band 65 is wound around theperiphery of the side wall of the faceplate 64.

An electron gun 66 for emitting electron beam Is arranged in the neck62. A phosphor screen 67 is formed on the inner surface of the faceplate64. The phosphor screen 67 is constituted by a phosphor layer which isexcited by electron beams from the electron gun 66 to emit light. Adeflection unit (not shown), which serves to deflect electron beams toscan over the phosphor screen, is arranged outside the cone 63.

A lower layer forming solution and an upper layer forming solution ofthe above Examples 1 to 7 are coated on the outer surface of thefaceplate 64 of the cathode ray tube 60, thus forming an antireflectionmultilayer film 68 having a two-layer structure according to the presentinvention.

In Example 1, the lower layer forming solution and the upper layerforming solution were coated by the dip method; however in this example,they were coated by spin coating method on the front surface of thefaceplate of the 25-inch color cathode ray tube after the completion ofthe assembly. The conditions for drying and calcination, and thethickness of each of the lower and upper layers were the same as thoseof Example 1.

Thus obtained antireflection film exhibited the characteristics shown inFIG. 1 to FIG. 7 of Examples 1 to 7. The cathode ray tube having theantireflection multilayer film hardly suffered reflection of ambientlight from a window, a lighting unit, and the like. In addition, sincereflection light became colorless light, a good images were formedwithout deteriorating in color reproduction property.

It should be noted that the spectral reflectance of the antireflectionmultilayer film formed on the surface of the color cathode ray tube wasmeasured by MCPD-1000 available from Otsuka Electronics k.k. A halogenlamp was used as a light source to perform measurement at an incidentangle of 0°. Then, a portion of the antireflection film was removed, andthe reflectance of that portion was measured. The value was expressedwith respect to that of the portion on which the antireflection film wasremoved assumed to be 100%. Also, the spectral transmittance wasmeasured by a spectrocolorimeter CM-1000 available from MINOLTA CAMERACO., LTD. Then, a portion of the antireflection multilayer film wasremoved by a chemical, and another measurement was performed on thatportion of the sample. The measurement value was expressed by the squareroot of the ratio of the value of the antireflection multilayer film tothe value of a portion on which antireflection multilayer film wasremoved.

EXAMPLE 11

As another example of the display apparatus, the case in which thepresent invention is applied to a liquid crystal display will now bedescribed.

FIG. 11 is a sectional view showing a liquid crystal apparatusmanufactured on the basis of the present invention.

The liquid crystal apparatus includes a pair of opposing glasssubstrates 71 and 72, the gap between which is regulated by a spacer 77made of thermosetting resin, and a liquid crystal 78 filled in the gap.Electrodes 73 and 74 having predetermined patterns and made of ITO(indium tin oxide) are formed on the opposing surfaces of the substrates71 and 72, and orientation films 75 and 76 are formed on theseelectrodes 73 and 74. The peripheral portions of the glass substrates 71and 72, between which the liquid crystal 78 is filled, are sealed by asealing agent 79.

In the liquid crystal display apparatus having the above-describedstructure, an antireflection multilayer film 80 is formed on the outersurface of the glass substrate 71. The antireflection multilayer film 80was formed as follows. After the peripheral portions of the substrates71 and 72 were sealed by the sealing agent 79, the lower layer formingsolution and the upper layer forming solution used in Example 3 werecoated to have a thickness of 0.1 82 m, followed by calcination. Theantireflection multilayer film 80 thus obtained exhibited an excellentantireflection property, as in the case of Example 3.

Although the present invention has been described with reference to theparticular embodiments, the antireflection characteristics of anantireflection multilayer film are to be properly set in accordance withcharacteristics required for a substrate on which the film is to beformed, and hence are not limited to those in the embodiments. Inaddition, combinations of antireflection films and display apparatus arenot limited to those in the above embodiments.

As described, according to the present invention, the multilayerantireflection film having an excellent antireflection property can bemanufactured simply by adding pigments to at least one layer of aantireflection film of a multilayer structure having two or more layers.Further, the present invention is industrially useful in terms ofselectivity of film material, and strength of film.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details, and representative devices, shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

What is claimed is:
 1. An antireflection film arrangement having amultilayer structure, comprising:a substrate; and an antireflectionmulti-layer film including at least two thin films formed on saidsubstrate, a first of said at least two films being an outermost thinfilm and being an odd-numbered film; wherein a second of said at leasttwo thin films contains a coloring material, said second film being aneven numbered film counting from said first outermost film, whereinodd-numbered films are free of said coloring material, wherein saidantireflection multi-layer film absorbs at least 5% of light in anentire range of wavelength of 400-700 nm, and wherein a reflectance ofsaid antireflection multi-layer film with regard to said range ofwavelength, light of which said antireflection multi-layer film canabsorb, is smaller than a reflectance of said substrate.
 2. Anantireflection film according to claim 1, wherein said antireflectionmulti-layer film absorbs at least 10% of light in said entire range ofwavelength of 400-700 nm.
 3. An antireflection film according to claim1, wherein said coloring material is at least one selected from thegroup consisting of carbon black and graphite.
 4. An antireflection filmaccording to claim 1, wherein said coloring material absorbs light insaid entire range of wavelength of 400-700 nm.
 5. An antireflection filmaccording to claim 1, wherein said thin films are made of one typeselected from the group consisting of SiO₂, TiO₂, ZrO₂, TaO₅, and Al₂O₃.
 6. An antireflection film according to claim 1, wherein said firstand second thin films have the same composition.
 7. An antireflectionfilm according to claim 1, wherein said first and second thin films havedifferent compositions.
 8. An antireflection film according to claim 1,wherein said even numbered films have a high refractive index, andwherein said odd numbered films have a low refractive index.
 9. Adisplay apparatus including an antireflection film arrangement having amulti-layer structure, comprising:a light-transmitting displaysubstrate; and an antireflection multi-layer film including at least twothin films formed on said substrate, a first of said at least two filmsbeing an outermost thin film and being an odd-numbered film; wherein asecond of said at least two thin films contains a coloring material,said second film being an even numbered film counting from said firstoutermost film, wherein odd-numbered films are free of said coloringmaterial, wherein said antireflection multi-layer film absorbs at least5% of light in an entire range of wavelength of 400-700 nm, and whereina reflectance of said antireflection multi-layer film relating to saidrange of wavelength, light of which said antireflection multi-layer filmcan absorb, is smaller than a reflectance of said substrate.
 10. Adisplay apparatus according to claim 9, wherein said display apparatusis a cathode ray tube.
 11. A display apparatus according to claim 9,wherein the display apparatus is a liquid crystal display apparatus. 12.A display apparatus according to claim 9, wherein said antireflectionmulti-layer film absorbs at least 10% of light in said entire range ofwavelength of 400-700 nm.
 13. A display apparatus according to claim 9,wherein said coloring agent is at least one selected from the groupconsisting of carbon black and graphite.
 14. A display apparatusaccording to claim 9, wherein said coloring material absorbs light insaid entire range of wavelength of 400-700 nm.
 15. A display apparatusaccording to claim 9, wherein said thin films are made of one typeselected from the group consisting of SiO₂, TiO₂, ZrO₂, TaO₅, and Al₂O₃.
 16. A display apparatus according to claim 9, wherein said first andsecond thin films have the same composition.
 17. A display apparatusaccording to claim 9, wherein said first and second thin films havedifferent compositions.
 18. A display apparatus according to claim 9,wherein said even numbered films have a high refractive index, andwherein said odd numbered films have a low refractive index.